Sealing arrangement for a flow machine

ABSTRACT

The present invention relates to a sealing arrangement for a flow machine. The sealing arrangement of the present invention is applicable for sealing bearing arrangements of centrifugal pumps, mixers, blowers etc. The present invention is especially applicable in sealing a bearing assembly including two angular contact ball bearings used in back-to-back configuration. The present invention relates especially to a baffle arranged between the bearing and the bearing housing, the baffle leaving a gap between itself and the inner bearing ring for the oil to flow from the bearing to the oil channel, and from the oil channel via a groove back to the oil chamber.

TECHNICAL FIELD

The present invention relates to a sealing arrangement for a flowmachine. The sealing arrangement of the present invention is applicablefor sealing bearing arrangements of centrifugal pumps, mixers, blowersetc. The present invention is especially applicable in sealing a bearingassembly including two angular contact ball bearings used inback-to-back configuration.

BACKGROUND ART

It is normal practice to use a pair of angular contact ball bearings inback-to-back configuration as a thrust bearing of a centrifugal pump.Such a thrust bearing is usually lubricated by means of an oil bath suchthat the oil level in an oil chamber at an axial side of the pair ofbearings extends to the centerline of the roller means at their lowestrotational position. The pair of angular contact ball bearings isusually positioned to the end of the flow machine closer to the couplingto the drive shaft and fastened on the shaft by means of a nut. Thebearing (of the pair of bearings) closer to the coupling, i.e. theoutermost bearing pumps the lubrication oil towards the bearing cover bymeans of which the bearings are affixed to the bearing housing. Themanufacturers of the bearings recommend that the thus pumped lubricationoil is returned to the oil chamber by means of a return groove or bore,which initiates from a local circular groove arranged in the bearinghousing at the axially outer end of the radially outer bearing ring.However, it is a commonly accepted fact that such a return groove orbore does not function in the manner desired, but the lubrication oilseems to collect against the bearing cover and to raise high, i.e.towards the axis of the shaft resulting in a flood at the area of theshaft sealing comprised normally of a lip type seal or a labyrinth seal.Very often such a flooding of the lubrication oil results in a leakageof the sealing. Naturally, such a leakage is problematic as graduallythe amount of lubrication oil in the oil chamber decreases and finallyresults in the dry running and breakage of the bearing. Additionally,leaking oil creates a harmful environmental risk.

Earlier the above discussed problem has been attempted to solve byimproving the sealing capability of the labyrinth seal used as the shaftseal against the pumped oil by designing and manufacturing a specificthrottling between the inner bearing ring and the labyrinth seal as isshown in FIG. 5 of U.S. Pat. No. B2-6,672,830. Such a throttling hasresulted in somewhat more effective sealing, but it has still beenobserved that especially at high rotational speeds it is not effectiveenough but the labyrinth seal starts leaking due to the bearing pumpingoil towards the seal.

WO 2010051959 discusses a construction where, between the bearing andthe bearing cover, there are two oil chambers separated from one anotherby means of a sealing ring leaving a narrow gap between itself and anaxial sleeve belonging to the labyrinth seal for oil to flow from thefirst chamber to the second one. In this construction the first chamberis adjacent the bearing and receives oil flow from the bearing. Thefirst chamber is provided with two passages for leading the oil awayfrom the first chamber. In case the first chamber receives more oil thanthe passages may take out the excess oil flows via the narrow gap to thesecond chamber, which is, also, provided with a passage for leading oilout of the second chamber. Problems relating to this constructionare: 1) that the volume of the first chamber is relatively large,whereby the oil is able to circulate round the volume, which meansincreased friction, heat generation and, as a consequence, high pumpingloss, and 2) that, irrespective of the volume of the first chamber, theconstruction has a high flow capacity for the oil due to the oil returnpassages from the first chamber, which also results in high frictionlosses in the various flow passages, high energy consumption and heatgeneration.

US 20080044279 discusses a shaft sealing where an isolated drain pathfor lubricant has been arranged between the bearing and the bearingcover. The drain path is formed of a first chamber adjacent the bearingto which chamber the oil flown through or pumped by the bearing mayfreely enter. The first chamber is limited at its side opposite to thebearing by means of a radial wall, which extends to the shaft leaving agap between itself and the shaft for oil to flow to the second chamber.The second chamber extends radially outwardly from the shaft andcontinues as an axial passage taking oil to the oil cavity. A problemwith this construction is the axial extension it requires. The USdocument does not discuss or show any means for locking the bearing onthe shaft, but in any case such means are needed. As the wall betweenthe first and the second chamber extends to the close proximity of theshaft the wall has to be arranged so far from the bearing that thelocking means may be left between the wall and the bearing, Thereforethe volume of the first chamber grows and the distance between thebearing and the bearing cover is increased. Another problem related tothe discussed construction is a high oil volume rotating in the firstchamber, which increases friction, energy consumption and heatgeneration.

BRIEF SUMMARY OF THE INVENTION

Thus an object of the present invention is to develop a new type ofshaft sealing for a flow machine capable of avoiding at least one of theabove discussed problems.

A further object of the present invention is to develop such a novelconstruction for a shaft sealing arrangement of a flow machine that iscapable of returning all the oil that enters in front of the shaftsealing via the bearings back to the oil chamber at the opposite side ofthe bearings.

A still further object of the present invention is to minimize thevolume of the chamber in which the oil enters from the bearing forkeeping the amount of oil in contact with the rotating parts of theshaft and bearing at its minimum.

Yet one more object of the present invention is to minimize the energyconsumption of the bearing by reducing the friction and heat generationinto its minimum.

At least one of the objects of the present invention is fulfilled by asealing arrangement for a flow machine, the flow machine comprising atleast an axis, a shaft, a thrust bearing formed of a pair of angularcontact ball bearings in back-to-back configuration, the ball bearingshaving an inner bearing ring and an outer bearing ring, a shaft sealing,a bearing cover at an outer end of the flow machine, an oil chamber atthe side of the thrust bearing opposite the bearing cover, a bafflearranged between the thrust bearing and the bearing cover for forming anoil channel between itself and the bearing cover, and a return groove orbore for returning oil from the oil channel to the oil chamber, whereinthere is a gap between the baffle and the inner bearing ring for theentire oil flow from the bearing to the oil channel and further to theoil chamber.

Other characterizing features of the sealing arrangement of the presentinvention become evident in the accompanying dependent claims.

BRIEF DESCRIPTION OF DRAWING

The sealing arrangement for a flow machine is described more in detailbelow, with reference to the accompanying drawings, in which

FIG. 1 illustrates an end part of a shaft of a flow machine with thethrust bearing and shaft sealing in accordance with prior art,

FIG. 1 a illustrates the shaft—thrust bearing—shaft seal assembly ofFIG. 1 in an enlarged scale,

FIG. 2 illustrates an end part of a shaft of a flow machine with thethrust bearing and shaft sealing in accordance a preferred embodiment ofthe present invention,

FIG. 2 a illustrates the shaft—thrust bearing—shaft seal assembly ofFIG. 2 in an enlarged scale,

FIG. 3 a illustrates the shaft—thrust bearing—shaft seal assembly of asecond preferred embodiment of the present invention in an enlargedscale, and

FIG. 3 b illustrates the shaft—thrust bearing—shaft seal assembly of athird preferred embodiment of the present invention in an enlargedscale.

DETAILED DESCRIPTION OF DRAWINGS

FIGS. 1 and 1 a illustrate a partial cross section of a prior art flowmachine 2 having a shaft 4, a pair of angular contact ball bearings 6 inback-to-back configuration and a shaft sealing 8. The pair of angularcontact ball bearings 6 acts as a thrust bearing of a flow machine, forinstance a centrifugal pump. The angular contact ball bearings areformed of an inner ring 6 i, an outer ring 6 o and bearing balls 10therebetween. The thrust bearing 6 has been fastened on the shaft 4 bytightening the inner rings 6 i against a shoulder on the shaft 4 bymeans of a nut 12 that is sometimes provided with a washer. The outerrings 6 o of the thrust bearing 6 are positioned against the innersurface of the bearing housing 14. Additionally, a bearing cover 16having a central hole for the shaft 4 and the shaft sealing 8 has beenfastened to the outer end of the bearing housing 14, i.e. to the end ofthe flow machine remove from the working member, for instance theimpeller of a centrifugal pump or the rotor of a mixer. The shaftsealing 8, here a labyrinth seal has been shown, though also lip-typeseals are sometimes used, is inserted in the central hole in the bearingcover 16. The bearing cover 16 is sealed by means of, for instance,O-rings in relation to both the shaft sealing 8 and the bearing housing14. The bearing housing 14 is provided with a groove 18 at the outer endthereof at the side of the outer bearing ring 6 o and a groove 20 orbore leading in more or less axial direction from the groove 18 to thecentral oil chamber 22. The oil level L in the oil chamber 22 extendsnormally up to the centerline of the bearing balls 10 as shown in FIG. 1a.

The above is the traditional structure of the thrust bearing—shaftsealing assembly of a flow machine. The same has also been shown in U.S.Pat. No. B2-6,672,830. However, as already discussed earlier, the shaftsealing of the assembly was apt to leak. The leakage related problem wastried to be solved by means of an improvement shown in FIGS. 1 and 1 a.The improvement in the shaft sealing 8 comprises a lip or an axialinward extension 24 of the shaft sealing 8 that leaves a narrowcircumferential gap 26 between itself and the radial side face of theinner thrust bearing ring 6 i. The purpose of the gap 26 is to restrictor to throttle the oil flow from the cavity 28 between the thrustbearing 6 and the bearing cover 16 towards the shaft.

However, now that the operation of the thrust bearing 6 comprising apair of angular contact ball bearings 6 in back-to-back configurationhas been thoroughly studied and understood it has been learned that evensuch a lip 24 and the gap 26 it creates with the inner bearing ring 6 icannot prevent the oil from entering the shaft sealing.

In other words, the right hand side ball bearing of the pair of angularcontact ball bearings 6 function such that the balls 10 running alongthe inner surface of the outer bearing ring 6 o squeezes oil from theoil film on the inner surface of the outer bearing ring 6 o axiallyoutwards. It means that the oil exiting the bearing ring surface has ahigh speed in axial direction (see arrow A in FIG. 1 a). The high speedof oil above the circular groove 18 results, in accordance withBernoulli's law, a reduction in the pressure (i.e. a partial vacuum)above the groove 18, which makes the oil flow along the groove 20 or acorresponding bore from the oil chamber 22 towards the shaft sealing,i.e. in a direction opposite to what the groove 20 or bore is originallypurposed for. In other words, the oil pumped by means of the bearingballs 10 axially out of the bearing reduces locally the pressure abovethe circular groove 18 to a value lower than the hydrostatic oilpressure in the oil chamber 22. Thus, the higher is the rotational speedof the shaft (or the bearing balls), the higher is the pressuredifference between the groove 18 and the oil chamber 22, and the higherthe oil level is raised in front of the shaft sealing 8 in cavity 28.Thereby it is clear that each prior art bearing assembly has its nominalspeed of rotation by which the oil level is raised up to the surface ofthe shaft 4, which means, when using labyrinth type sealing, oil leakagethrough the sealing. When the operation of the angular contact ballbearings is understood in this detail it is also easy to understand thatthe throttling or gap 26 has little if any effect on preventing theleakage.

FIGS. 2 and 2 a illustrate a preferred embodiment of the presentinvention solving both the problem discussed in connection with FIGS. 1and 1 a and the problems referred to in the background art. Now that theprior art problem leading to the increased risk of oil leakage was dueto bearing balls 10 pumping oil at a high speed transverse across thegroove/channel that was designed for the removal of oil, and thuscreating a partial vacuum there, the problem is solved by cutting thedirect flow connection between the interior of the bearing and the oilreturn groove or bore. It has been accomplished by either redesigningthe bearing cover 30 to include a baffle 32 or by arranging a separatebaffle between the bearing cover and the thrust bearing 6. Theembodiment shown in FIGS. 2 and 2 a discloses a bearing cover 30 with abaffle 32 forming a part of the bearing cover 30. In this embodiment thebearing cover 30 extends axially up to the radial face of the outerbearing ring 6 o (of the right hand side angular contact ball bearing orthe angular contact ball bearing facing the bearing cover or the outerend of the flow machine or that of the bearing housing) and has aradially inwardly (towards the shaft 4) directed baffle 32 that extendsto the side of the inner bearing ring 6 i (of the right hand sideangular contact ball bearing or the angular contact ball bearing facingthe bearing cover or the outer end of the flow machine or that of thebearing housing) such that the distance D2 from the axis of the flowmachine to the inner surface 34 of the baffle 32 is smaller than theouter radius of the inner bearing ring 6 i. Thus, a axial gap 36 isformed between the baffle 32 and the radial side face of the innerbearing ring 6 i. The dimension of the gap 36 is preferably, but notnecessarily, about 0.2-0.7 mm depending on the size of the bearings,rotational speed of the flow machine, etc. The baffle 32 and the part ofthe bearing cover 30 forming the axially outer face of the flow machine,or the bearing housing, leave a groove-like channel 38 therebetween, thechannel 38 being open towards the shaft 4. The bottom of the channel 38is provided with a bore 40 extending through the bearing cover 30 to apreferably axial groove 20 arranged in the inside surface of the bearinghousing 14. The groove 20 may be replaced with an axial or slightlyinclined bore if desired. The bore 40 and the groove 20 or bore functionas the oil return passage in case oil from the thrust bearing 6 entersthe channel 38 between the baffle 32 and the rest of the bearing cover30.

The above described bearing cover construction solves the problemrelating to the oil leakage by means of preventing the directcommunication of the oil in the bearing 6 and the oil in the returngroove 20. Now, in accordance with this preferred embodiment of thepresent invention, if the oil pressure is raised in the cavity betweenthe bearing balls 10 and the baffle 32 due to the pumping effect of theballs the entire oil flow from the bearing 6 to the oil channel 38 andfurther to the oil chamber 22 is forced through the gap 36 between thebaffle 32 and the inner bearing ring 6 i and round the circumferentialinner edge or inner surface 34 of the baffle 32 into the channel 38.However, the channel 38 of the present invention is an open cavityhaving no specific pressure conditions unlike the groove 18 of the priorart flow machine where a partial vacuum created in the groove 18 wasdrawing oil from the groove 20. Thus, as the inner circumference orinner surface 34 of the baffle 32 extends closer (dimension D2) to theaxis of the flow machine than the oil level L (dimension D1), the oilentering the channel 38 raises the oil level in the channel whereafterthe oil is able to return via the bore 40 and the groove 20 back to theoil chamber 22 as soon as the hydrostatic pressure in the channel 38 ishigher than that in the oil chamber 22.

In other words, in the arrangement of the present invention the returnchannel 38 of the oil has been moved to an open position far from therotary members and other areas of high flow velocity which would have anegative effect on the functioning of the return channel 38. The returnbore 40 and the return groove 20 have to be dimensioned large enough tobe capable of handling the entire oil flow.

It should also be understood that as the baffle 32 is at a small axialdistance of less than 1 mm from the inner bearing ring, the volume ofthe cavity where the oil is rotating is minimized. This results inminimized oil circulation between the baffle and the bearing and therebyto minimized friction, energy consumption and heat generation.

As already mentioned above the bearing cover and the baffle may also beseparate parts as shown in FIGS. 3 a and 3 b. However, the functionalpart of the baffle i.e. the radially innermost part of the baffle isalways the same, especially its dimensioning in relation to both theouter diameter of the inner bearing ring and the distance between theoil level in the oil chamber from the axis, as well as its distance fromthe inner bearing ring. Thus only the foot part i.e. the radially outerpart of the baffle may vary. In accordance with FIG. 3 a the separatebaffle 32′ is pressed by the bearing cover 30 against the radially outerring 6 o of the axially outer bearing. In accordance with FIG. 3 b thebaffle 32″ is a separate part, preferably a ring arranged inside thebearing cover 30 between the bearing 6 and the bearing cover 30. Thebaffle 32″ may extend axially from the bearing cover 30 to the level ofthe bearing or at a distance thereof (shown in FIG. 3 b). In one furthernot illustrated embodiment the baffle is a separate member, like in FIG.3 b, but now it leaves an axial gap between itself and the bearingcover, whereby the gap may function as the oil channel 38. Preferablythe baffle is, in its all structural alternatives a circular membersurrounding the shaft of the flow machine, whereby also the channel 38between the baffle and the (rest) of the bearing cover is a circularchannel. However, the groove 20 or the corresponding bore and the bore40 at the bottom of the channel 38 are located at the lowermostpositions of the inner surface of the bearing housing 14, and thechannel 38, respectively, for ensuring the best possible recirculationof oil back to the central oil chamber.

As can be seen from the above description a novel shaft sealingarrangement has been developed. While the invention has been hereindescribed by way of examples in connection with what are at presentconsidered to be the preferred embodiments, it is to be understood thatthe invention is not limited to the disclosed embodiments, but isintended to cover various combinations and/or modifications of itsfeatures and other applications within the scope of the invention asdefined in the appended claims.

1. A sealing arrangement for a flow machine, the flow machine comprisingat least an axis, a shaft (4), a thrust bearing (6) formed of a pair ofangular contact ball bearings in back-to-back configuration, the ballbearings having an inner bearing ring (6 i) and an outer bearing ring (6o), a shaft sealing (8), a bearing cover (30) at an outer end of theflow machine, an oil chamber (22) at the side of the thrust bearing (6)opposite the bearing cover (30), a baffle (32, 32′, 32″) arrangedbetween the thrust bearing (6) and the bearing cover (30) for forming anoil channel (38) between itself and the bearing cover (30), and a returngroove (20) or bore for returning oil from the oil channel (38) to theoil chamber (22), characterized in a gap (36) between the baffle (32,32′, 32″) and the inner bearing ring (6 i) for the entire oil flow fromthe bearing to the oil channel (38) and further to the oil chamber (22).2. The sealing arrangement as recited in claim 1, characterized in thatthe baffle (32, 32′) is positioned against the outer bearing ring (6 i),the baffle (32, 32′) extending radially inwardly to the side of theinner bearing ring (6 i) leaving the gap (36) therebetween.
 3. Thesealing arrangement as recited in claim 1, characterized in that thebaffle (32, 32′, 32″) has an inner circumference or surface (34) thediameter of which is smaller than the outer diameter of the innerbearing ring (6 i).
 4. The sealing arrangement as recited in claim 1,characterized in that, when in use, the baffle (32, 32′, 32″) has aninner circumference or surface (34) the diameter D2 of which is smallerthan the distance D1 from the oil level L to the axis of the flowmachine.
 5. The sealing arrangement as recited in claim 1, characterizedin that the baffle (32, 32′) is arranged to rest against the radial sidesurface of the outer bearing ring (6 o).
 6. The sealing arrangement asrecited in claim 1, characterized in that the baffle (32′) is a separatecircular ring arranged between the bearing cover (30) and the outerbearing ring (6 o).
 7. The sealing arrangement as recited in claim 1,characterized in that the baffle (32″) is a separate circular ringarranged between the bearing (6) and the bearing cover (30).
 8. Thesealing arrangement as recited in claim 1, characterized in that thebaffle (32) is a part of the bearing cover (30).
 9. The sealingarrangement as recited in claim 1, characterized in that the gap (36)between the baffle (32, 32′, 32″) and the inner bearing ring (6 i) has adimension of 0.2-0.7 mm.